A proxy server is a server, a computer system or an application program which works like a gateway between a client and a web server.
A client connects to the proxy server to request a web page from a different server. Then the proxy server provides the resource by connecting to the specified server. A proxy server can be used by companies or universities to cache Web content. When for example 100 people in the local network request the website http://www.yahoo.com/ during one hour, the request is only sent once to yahoo.com. The other 99 times the request is provides by the proxy server. That way the company or university saves traffic (costs) but can also filter the requests.
Regarding Internet censorship a proxy server fullfils 2 functions:
- A user has to connect through a proxy server where his requests are filtered
- Proxies are also the most common way to bypass censorship
so depending on the kind of proxy server they can be "bad" or "good" for us.
Sometimes the ISP is using a transparent proxy. When using these you don't have to enter and so also won't find any proxy adresses. In your connection settings you can find out if you are using a transparent proxy by visiting a ProxyJudge website and compare the "REMOTE_ADDR" value with the one you get when you type "ipconfig" in your DOS-prompt. If its the same, you use no proxy. And if its different you use a proxy. Either a forced proxy with the adress and port in your browser settings or else a transparent one.